Scheduling method for device-to-device communication and apparatus for same

ABSTRACT

The present invention relates to a wireless communication system. More particularly, the present invention relates to a method for transmitting device-to-device (D2D) data and an apparatus therefor, the method comprising the steps of: receiving, from a base station, control information which includes a first resource allocation information item; transmitting, to a second terminal, a second physical downlink control channel (PDCCH) signal which includes a second resource allocation information item, while including the resource indicated by the second resource allocation information item in the resource indicated by the first allocation information item; and transmitting the D2D data to the second terminal by using the resource indicated by the second resource allocation information item.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT/KR2013/005565 filed onJun. 24, 2013, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/662,922 filed on Jun. 22, 2012, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present invention relates to a wireless communication method, andmore particularly, to a scheduling method and apparatus fordevice-to-device (D2D) communication.

BACKGROUND ART

Wireless communication systems have been widely deployed in order toprovide various types of communication services including voice or data.In general, a wireless communication system is a multiple access systemthat can support communication with multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.). Examples ofmultiple access systems include a code division multiple access (CDMA)system, a frequency division multiple access (FDMA) system, a timedivision multiple access (TDMA) system, an orthogonal frequency divisionmultiple access (OFDMA) system, a single carrier frequency divisionmultiple access (SC-FDMA), etc.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method and apparatus for effectively transmitting control informationin a wireless communication system. Another object of the presentinvention devised to solve the problem lies in a method and apparatusfor effectively transmitting control information in a system forsupporting user equipment (UE)-UE link and effectively managingresources for the effective transmission.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting Device-to-Device (D2D) data by a first userequipment (UE) in a wireless communication system, the methodcomprising: receiving control information including first resourceallocation information from a base station; transmitting a secondPhysical Downlink Control Channel (PDCCH) signal including secondresource allocation information to a second UE, wherein a resourceindicated by the second resource allocation information is included aresource indicated by the first resource allocation information; andtransmitting the D2D data to the second UE using the resource indicatedby the second resource allocation information.

In another aspect of the present invention, provided herein is a firstuser equipment (UE) configured to perform Device-to-Device (D2D)operations in a wireless communication system, the first UE including aradio frequency (RF) unit and a processor, wherein, the processor isconfigured to receive control information including first resourceallocation information from a base station, to transmit a secondPhysical Downlink Control Channel (PDCCH) signal including secondresource allocation information to a second UE, wherein a resourceindicated by the second resource allocation information is included aresource indicated by the first resource allocation information, and totransmit the D2D data to the second UE using the resource indicated bythe second resource allocation information.

The first resource allocation information may be included in a firstPDCCH signal, and a Cyclic Redundancy Check (CRC) of the first PDCCHsignal may be scrambled with a common Radio Network Temporary Identifier(RNTI) for D2D.

The first resource allocation information may be included in a PhysicalDownlink Shared Channel (PDSCH) signal, and the PDSCH may includeidentification information for a plurality of D2D UEs and a plurality ofresource allocation information corresponding to the plurality of D2DUEs.

The resource indicated by the second resource allocation information maybe allocated on assumption that the resource indicated by the firstresource allocation is an entire resource for D2D communication.

The first resource allocation may indicate a plurality of frequencyresources indexes, and the plurality of frequency resources indexes arerenumbered for the second resource allocation information.

A field size of the second resource allocation information may besmaller than a field size of the first resource allocation information.

Advantageous Effects

According to the present invention, control information can beeffectively transmitted in a wireless communication system. In detail,in a system for supporting device-to-device (D2D) communication,scheduling information can be effectively transmitted and resources forthe transmission can be effectively managed.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description taken in conjunction with theaccompanying drawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram showing physical channels used in a 3GPP LTE(-A)system and a general signal transmission method using the same;

FIG. 2 is a diagram for explanation of a single carrier frequencydivision multiple access (SC-FDMA) method and an orthogonal frequencydivision multiple access (OFDMA) method;

FIG. 3 is a diagram showing the structure of a radio frame;

FIG. 4 illustrates a resource grid of a downlink slot;

FIG. 5 illustrates a downlink subframe structure;

FIG. 6 illustrates an example in which a physical downlink controlchannel (PDCCH) is allocated to a data region of a subframe;

FIG. 7 illustrates a downlink reference signal (RS) pattern;

FIG. 8 illustrates a structure of a demodulation reference signal (DMRS)(or a UE-specific RS) structure;

FIG. 9 illustrates a structure of an uplink subframe;

FIG. 10 illustrates a uplink hybrid automatic repeat request (UL HARQ)operation;

FIG. 11 illustrates a system for supporting device-to-device (D2D) link;

FIGS. 12 to 14 illustrate a procedure for performing D2D communicationaccording to the present invention; and

FIG. 15 illustrates a base station and a user equipment (UE) to which anembodiment of the present invention is applicable.

BEST MODE

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), orthogonal frequency division multipleaccess (OFDMA), single carrier frequency division multiple access(SC-FDMA), and the like. CDMA may be embodied through wireless (orradio) technology such as universal terrestrial radio access (utra) orCDMA2000. TDMA may be embodied through wireless (or radio) technologysuch as global system for mobile communication (GSM)/general packetradio service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMAmay be embodied through wireless (or radio) technology such as instituteof electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, and evolved UTRA (E-UTRA). UTRA is a partof universal mobile telecommunications system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of E-UMTS(Evolved UMTS), which uses E-UTRA. 3GPP LTE employs OFDMA in downlinkand employs SC-FDMA in uplink. LTE-Advanced (LTE-A) is an evolvedversion of 3GPP LTE.

For clarity, the present invention will be described in terms of 3GPPLTE/LTE-A, but is not limited thereto. Specific terms used in theembodiments of the present invention are provided to aid in theunderstanding of the present invention. These specific terms may bereplaced with other terms within the scope and spirit of the presentinvention.

In a wireless communication system, a UE receives information from aneNB through downlink (DL) and transmits information to the eNB throughuplink (UL). Information transmitted/received between the UE and eNBincludes data and various types of control information, and variousphysical channels are present according to type/purpose of informationtransmitted/received between the UE and eNB.

FIG. 1 is a diagram showing physical channels used in a 3GPP LTE(-A)system and a general signal transmission method using the same.

When a UE is powered on or enters a new cell, the UE performs an initialcell search operation such as synchronization with an eNB in step S101.To this end, the UE may receive a primary synchronization channel(P-SCH) and a secondary synchronization channel (S-SCH) from the eNB toperform synchronization with the eNB and acquire information such as acell ID. Then, the UE may receive a physical broadcast channel from theeNB to acquire broadcast information in the cell. During the initialcell search operation, the UE may receive a downlink reference signal(DL RS) so as to confirm a downlink channel state.

After the initial cell search operation, the UE may receive a physicaldownlink control channel (PDCCH) and a physical downlink control channel(PDSCH) based on information included in the PDCCH to acquire moredetailed system information in step S102.

When the UE initially accesses the eNB or has no radio resources forsignal transmission, the UE may perform a random access procedure (RACH)with respect to the eNB in steps S103 to S106. To this end, the UE maytransmit a specific sequence as a preamble through a physical randomaccess channel (PRACH) (S103) and receive a response message to thepreamble through the PDCCH and the PDSCH corresponding thereto (S104).In the case of contention-based RACH, the UE may perform a contentionresolution procedure by further transmitting the PRACH (S105) andreceiving a PDCCH and a PDSCH corresponding to the PDCCH (S106).

After the above procedure, the UE may receive PDCCH/PDSCH from the eNB(S107) and may transmit a PUSCH/PUCCH to the eNB (S108), as a generaluplink/downlink signal transmission procedure. Here, control informationtransmitted from the UE to the eNB is called uplink control information(UCI). The UCI may include a hybrid automatic repeat and requestacknowledgement/negative-ack (HARQ ACK/NACK) signal, scheduling request(SR), channel state information (CSI), etc. The CSI includes a channelquality indicator (CQI), a precoding matrix indicator (PMI), rankindication (RI), etc. While the UCI is transmitted through a PUCCH ingeneral, it may be transmitted through a PUSCH when control informationand traffic data need to be simultaneously transmitted. The UCI may beaperiodically transmitted through a PUSCH according to therequest/instruction of a network.

FIG. 2 is a diagram for explanation of an SC-FDMA method and an OFDMAmethod. A 3GPP system adopts OFDMA for downlink and SC-FDMA for uplink.

Referring to FIG. 2, a UE for uplink signal transmission and a eNB fordownlink signal transmission are the same in that both the UE and theeNB include a serial-to-parallel converter 401, a subcarrier mapper 403,an M-point IDFT module 404, and a CP attaching module 406. However, a UEfor signal transmission via an SC-FDMA method further include an N-pointDFT module 402. The N-point DFT module 402 may partly offset influenceof IDFT processing of an M-point IDFT module 404 such that a transmittedsignal has single subcarrier characteristics.

FIG. 3 is a diagram showing the structure of a radio frame.Uplink/downlink data packets are transmitted in units of subframes. Onesubframe is defined as a predetermined time period including a pluralityof OFDM symbols. LTE(-A) supports a type-1 radio frame structureapplicable to frequency division duplex (FDD) and a type-2 radio framestructure applicable to time division duplex (TDD).

FIG. 3(a) illustrates the type-1 radio frame structure. Adownlink/uplink radio frame is divided into 10 subframes. Each subframeis further divided into two slots in the time domain. For example, onesubframe may be 1 ms in duration and one slot may be 0.5 ms in duration.A slot includes a plurality of OFDM symbols (or SC-FDMA symbols) in thetime domain and a plurality of resource blocks (RBs) in the frequencydomain. The LTE(-A) system adopts OFDMA for downlink and SC-FDMA foruplink. An RB is a resource allocation unit including a plurality ofcontiguous subcarriers in one slot.

FIG. 3(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes. Each subframeis divided into two slots. In a TDD mode, a subframe in a radio frame isconfigured as D, U, or S according to uplink-downlink (UL-DL)configuration. Here, D denotes a downlink subframe, U denotes an uplinksubframe, and S denotes a special subframe. The special subframeincludes downlink pilot timeslot (DwPTS), guard period (GP), and uplinkpilot timeslot (UpPTS). The DwPTS is a period reserved for downlinktransmission and the UpPTS is a period reserved for uplink transmission.

FIG. 4 illustrates a resource grid of a downlink slot.

Referring to FIG. 4, a downlink slot includes a plurality of OFDMsymbols in the time domain. One downlink slot may include 7(6) OFDMsymbols, and one resource block (RB) may include 12 subcarriers in thefrequency domain. Each element on the resource grid is referred to as aresource element (RE). One RB includes 12×7(6) REs. The number N_(RB) ofRBs included in the downlink slot depends on a downlink transmitbandwidth. The structure of an uplink slot may be same as that of thedownlink slot except that OFDM symbols are replaced by SC-FDMA symbols.

FIG. 5 illustrates a downlink subframe structure.

Referring to FIG. 5, a maximum of three (four) OFDM symbols located in afront portion of a first slot within a subframe correspond to a controlregion to which a control channel is allocated. The remaining OFDMsymbols correspond to a data region to which a physical downlink sharedchancel (PDSCH) is allocated. Examples of downlink control channels usedin LTE include a physical control format indicator channel (PCFICH), aphysical downlink control channel (PDCCH), a physical hybrid ARQindicator channel (PHICH), etc. The PCFICH is transmitted at a firstOFDM symbol of a subframe and carries information regarding the numberof OFDM symbols used for transmission of control channels within thesubframe. The PHICH is a response of uplink transmission and carries anHARQ acknowledgment (ACK)/not-acknowledgment (NACK) signal. The HARQ-ACKrefers to a reception response result for downlink transmission (e.g.,physical downlink shared channel (PDSCH) or semi-persistent schedulingrelease physical downlink control channel (SPS release PDCCH), that is,ACK/NACK/DTX response (simply, ACK/NACK response, ACK/NACK, A/Nresponse, and A/N). The A/N refers to ACK, NACK, DTX, or NACK/DTX. ThePDSCH may be replaced by a transport block or a codeword.

Control information transmitted through the PDCCH is referred to asdownlink control information (DCI). Formats 0, 3, 3A and 4 for uplinkand formats 1, 1A, 1B, 1C, 1D, 2, 2A, 2B and 2C for downlink are definedas DCI formats. The DCI formats selectively include information such ashopping flag, RB allocation, modulation coding scheme (MCS), redundancyversion (RV), new data indicator (NDI), transmit power control (TPC),cyclic shift for demodulation reference signal (DMRS), channel qualityinformation (CQI) request, HARQ process number, transmitted precodingmatrix indicator (TPMI), precoding matrix indicator (PMI), etc.confirmation according as necessary.

A PDCCH may carry a transport format and a resource allocation of adownlink shared channel (DL-SCH), resource allocation information of anuplink shared channel (UL-SCH), paging information on a paging channel(PCH), system information on the DL-SCH, information on resourceallocation of an upper-layer control message such as a random accessresponse transmitted on the PDSCH, a set of Tx power control commands onindividual UEs within an arbitrary UE group, a Tx power control command,information on activation of a voice over IP (VoIP), etc. A plurality ofPDCCHs can be transmitted within a control region. The UE can monitorthe plurality of PDCCHs. The PDCCH is transmitted on an aggregation ofone or several consecutive control channel elements (CCEs). The CCE is alogical allocation unit used to provide the PDCCH with a coding ratebased on a state of a radio channel. The CCE corresponds to a pluralityof resource element groups (REGs). A format of the PDCCH and the numberof bits of the available PDCCH are determined by the number of CCEs. TheeNB determines a PDCCH format according to DCI to be transmitted to theUE, and attaches a cyclic redundancy check (CRC) to control information.The CRC is masked with a unique identifier (referred to as a radionetwork temporary identifier (RNTI)) according to an owner or usage ofthe PDCCH. For example, if the PDCCH is for a specific UE, a uniqueidentifier (e.g., cell-RNTI (C-RNTI)) of the UE may be masked to theCRC. Alternatively, if the PDCCH is for a paging message, a pagingidentifier (e.g., paging-RNTI (P-RNTI)) may be masked to the CRC. If thePDCCH is for system information (more specifically, a system informationblock (SIB)), a system information RNTI (SI-RNTI) may be masked to theCRC. When the PDCCH is for a random access response, a randomaccess-RNTI (RA-RNTI) may be masked to the CRC.

As described above, in the LTE system, an FDD DL carrier and TDD DLsubframes use first n OFDM symbols of a subframe for transmission of aPDCCH, a PHICH, a PCFICH, etc. as a physical channel for transmission ofvarious pieces of control information and use the remaining OFDM symbolsfor PDSCH transmission. In each subframe, the number of symbols used forcontrol channel transmission is dynamically transmitted to a UE througha physical channel such as a PCFICH, etc. or is semi-staticallytransmitted to the UE via RRC signaling. n may be set up to four symbolsfrom one symbol according to subframe characteristics and systemcharacteristics (FDD/TDD, a system bandwidth, etc.). In the legacy LTEsystem, there is a limit in that a PDCCH as a physical channel for DL/ULscheduling and transmission various pieces of control information istransmitted through limited OFDM symbols. Thus, the LTE-A systemadditionally introduces an enhanced PDCCH (E-PDCCH) that is more freelymultiplexed in PDSCH and FDM manners.

FIG. 6 illustrates an example in which a downlink physical channel isallocated to a subframe.

Referring to FIG. 6, a PDCCH (for convenience, legacy PDCCH and L-PDCCH)according to the legacy LET may be allocated to a control region (referto FIG. 5) of a subframe. In FIG. 6, the L-PDCCH region refers to aregion to which the legacy PDCCH can be allocated. According to thecontext, the L-PDCCH region may refer to a control region, a controlchannel resource region (i.e., CCE resource) to which a PDCCH can beactually allocated in the control region, or a PDCCH search space. APDCCH in a data region (e.g., a resource region for a PDSCH, refer toFIG. 5) can be additionally allocated. The PDCCH allocated to a dataregion is referred to as an E-PDCCH. As illustrated in FIG. 6, a controlchannel resource can be additionally ensured through an E-PDCCH so as toalleviate scheduling restraints due to a limited control channelresource of the L-PDCCH region.

Like an L-PDCCH, an E-PDCCH carriers DCI. For example, the E-PDCCH maycarrier downlink scheduling information and uplink schedulinginformation. The E-PDCCH/PDSCH procedure and the E-PDCCH/PUSCH procedureare the same/similar to those described with reference to steps S107 andS108 of FIG. 1. That is, the UE may receive an E-PDCCH and receivedata/control information through a PDSCH corresponding to the E-PDCCH.In addition, the UE may receive the E-PDCCH and transmit data/controlinformation through a PUSCH corresponding to the E-PDCCH. The legacy LTEadopts a method for pre-reserving a PDCCH candidate region (hereinafter,a PDCCH search space) in a control region and transmitting a PDCCH of aspecific UE to a portion of the PDCCH search space. Accordingly, the UEmay acquire a PDCCH of the UE in the PDCCH search space via blinddecoding. Similarly, the E-PDCCH may also be partially or entirelytransmitted over the pre-reserved resource.

FIG. 7 illustrates a downlink reference signal (RS) pattern of an LTEsystem.

Referring to FIG. 7, in the LTE system, two types of downlink RSs aredefined for unicast services. Common RSs (CRS) R0 to R3 for acquisitionof information regarding channel state and measurement of handover and aUE-specific CRS ‘D’ for data demodulation are present. A UE-specific RSis referred to as a dedicated RS (DRS). The UE-specific RS is used onlyfor data demodulation and the CRS is used both for acquisition ofchannel information and data demodulation. The CRS is a cell-specificsignal and is transmitted every subframe through a whole band. The LTEsystem supports a maximum of 4 transmission antennas for downlink, andthus a CRS for a maximum of 4 antenna ports can be transmitted accordingto the number of transmission antennas. A CRS for each antenna port ismultiplexed in an RB using a frequency division multiplexing (FDM)method.

A set of some of all subframes may be configured as a multicastbroadcast single frequency network (MBSFN) subframe. The MBSFN subframeis a subframe configured for transmission of multicast/broadcastsignals. The MBSFN subframe may be periodically configured. In the caseof MBSFN subframe, a CRS is transmitted through only first and secondOFDM symbols, and a UE that is not configured with an MBSFN service maydisregard a data region or may not receive the data region.

FIG. 8 illustrates a structure of a DMRS added to an LTE-A system. TheDMRS is a UE-specific RS used for demodulation of a signal of each layerwhen a signal is transmitted using a multiple antenna. The DMRS is usedfor PDSCH demodulation. The LTE-A system considers a maximum of 8transmission antennas, and thus a maximum of 8 layers and respectiveDM-RSs therefor are required.

Referring to FIG. 8, DMRSs for two or more layers share the same RE andare multiplexed using a code division multiplexing (CDM) method. Indetail, a DM-RS for each layer is spread using a spreading code (e.g.,an orthogonal code such as Walsh code and DFT code) and then multiplexedon the same RE. For example, DMRSs for layers 0 and 1 share the same RE.The DMRSs are spread using an orthogonal code in two REs of OFDM symbols#12 and #13 in a subcarrier #1 (k=1), for example. That is, in eachslot, DMRS for layers 0 and 1 are spread along the time axis using acode with a spreading factor (SF)=2 and then multiplexed on the same RE.For example, the DMRS for a layer #0 can be spread using [+1 +1] and theDMRS for a layer #1 can be spread using [+1 −1]. Similarly, DMRSs forlayers #2 and #3 are spread using different orthogonal codes on the sameRE. DMRSs for layers #4, #5, #6 and #7 are spread on REs occupied byDMRSs #0, #1, #2 and #3 using a code orthogonal to layers #0, #1, #2 and#3. A code with SF=2 is used for up to 4 layers and a code with SF=4 isused for DMRS for 5 or more layers. Antenna ports for DMRS correspond to{7, 8, . . . , n+6} (n being the number of layers).

FIG. 9 illustrates a structure of an uplink subframe used in LTE(-A).

Referring to FIG. 9, a subframe 500 is composed of two 0.5 ms slots 501.Assuming a length of a normal cyclic prefix (CP), each slot is composedof 7 symbols 502 and one symbol corresponds to one SC-FDMA symbol. Aresource block (RB) 503 is a resource allocation unit corresponding to12 subcarriers in the frequency domain and one slot in the time domain.The structure of the uplink subframe of LTE(-A) is largely divided intoa data region 504 and a control region 505. A data region refers to acommunication resource used for transmission of data such as voice, apacket, etc. transmitted to each UE and includes a physical uplinkshared channel (PUSCH). A control region refers to a communicationresource for transmission of an uplink control signal, for example,downlink channel quality report from each UE, reception ACK/NACK for adownlink signal, uplink scheduling request, etc. and includes a physicaluplink control channel (PUCCH). A sounding reference signal (SRS) istransmitted through an SC-FDMA symbol that is lastly positioned in thetime axis in one subframe. SRSs of a plurality of UEs, which aretransmitted to the last SC-FDMAs of the same subframe, can bedifferentiated according to frequency positions/sequences.

Hereinafter, hybrid automatic repeat request (HARQ) will be described.In a wireless communication system, when a plurality of UEs having datato be transmitted in uplink/downlink is present, an eNB selects a UE towhich data is to be transmitted every transmission time interval (TTI)(e.g., subframe). In a multicarrier system and a system managed in asimilar way thereto, an eNB selects UEs to which data is to betransmitted in uplink/downlink every TTI and also selects a frequencyband used for data transmission by the corresponding UE.

In terms of uplink, UEs transmits an RS (or pilot) in uplink and an eNBrecognizes a channel state of the UEs using the RS transmitted from theUEs and selects UEs to which data is to be transmitted in uplink in eachunit frequency band every TTI. The eNB notifies a UE of this result.That is, the eNB transmits an uplink assignment message indicating thatdata is to be transmitted using a specific frequency band to a UE thatis uplink-scheduled to a specific TTI. The uplink assignment message isalso referred to as UL grant. The UE transmits data in uplink accordingto the uplink assignment message. The uplink assignment message mayinclude a UE identify (ID), RB allocation information, a modulation andcoding scheme (MCS), a redundancy version (RV), new data indication(NDI), etc.

In the case of a synchronous non-adaptive HARQ method, retransmissiontime is systemically determined (e.g., after 4 subframes from an NACKreception point of time). Thus, a UL grant message transmitted to a UEby an eNB is transmitted only at initial transmission and nextretransmission is performed by ACK/NACK signals (e.g., a PHICH signal).On the other hand, in the case of asynchronous adaptive HARQ method,retransmission time is not determined, and thus the eNB needs totransmit a retransmission request message to the UE. In addition, an MCSor a frequency resource for retransmission is varied every transmissiontime, and thus the retransmission request message may include a UE ID,RB allocation information, an HARQ process index, RV, and NDIinformation.

FIG. 10 illustrates a UL HARQ operation in an LTE(-A) system. In theLTE(-A) system, a UL HARQ method uses synchronous non-adaptive HARQ.When 8 channel HARQ is used, an HARQ process number is given as 0 to 7.One HARQ process is operated every TTI (e.g., subframe). Referring toFIG. 10, an eNB 110 transmits UL grant to a UE 120 through a PDCCH(S600). The UE 120 transmits uplink data to the eNB 110 using an MCS andan RB determined by UL grant after four subframes (e.g., subframe #4)from reception point of time of the UL grant (S602). The eNB 110 decodesuplink data received from the UE 120 to generate ACK/NACK. Upon failingto decode the uplink data, the eNB 110 transmits NACK to the UE 120(S604). The UE 120 retransmits uplink data after four subframes from areception point of time of NACK (S606). Initial transmission andretransmission of uplink data are performed by the same HARQ processor(e.g., HARQ process 4). ACK/NACK information may be transmitted througha PHICH.

Embodiment

FIG. 11 illustrates a wireless communication system for supportingdevice-to-device (D2D) communication. In the case of legacy LTE andLTE-A systems, UEs are scheduled from an eNB for communication betweenthe UEs and also perform a series of processes for transmitting andreceiving data through the eNB. On the other hand, (although controlfrom the eNB is also partially performed,) a communication scheme fortransmitting and receiving directly to and from the UE without passingthrough the eNB is referred to as D2D communication or UE-UEcommunication. Referring to FIG. 11, in a user plane, UE2 may performdirect communication with UE1 without passing through a network (e.g.,an eNB) (UE-UE communication/link). In addition, in the user plane, UE2may perform communication with another UE through an eNB according to aconventional method (UE-eNB link/communication).

Hereinafter, the present invention proposes a scheduling process for D2Dcommunication and D2D resource allocation performed together therewith,and a D2D signal modulation and demodulation scheme.

For convenience, a device for performing a D2D data transmissionoperation on D2D communication link is referred to as a transmissiondevice (TD) and a device for performing a D2D data reception operationis referred to as a receiving device (RD). Unless mentioned otherwise,in the present invention, a PDCCH include both a legacy L-PDCCH and anE-PDCCH and can be interpreted according to the context.

(1) Scheduling Procedure for D2D Communication

FIG. 12 illustrates the case in which a scheduling procedure for D2Dcommunication, in detail, scheduling for D2D communication is performedwith intervention of an eNB according to an embodiment of the presentinvention. Referring to FIG. 12, the eNB may provide information and/ora parameter required for D2D communication to UEs (e.g., UE1 and UE2)configured to perform D2D communication ((a) {circle around (1)} and (b){circle around (1)}). Then actual scheduling for D2D communication mayinclude two types of methods. A first method is similar to aconventional DL scheduling method, TD (UE1) may transmit informationrequired for scheduling to RD (UE2) ((a){circle around (2)}) andtransmit D2D data corresponding thereto ((a){circle around (3)}). Asecond method is similar to a conventional UL scheduling method, TD(UE1)may receive information required for scheduling from RD (UE2)((b){circle around (2)}) and transmit D2D data corresponding thereto((b){circle around (3)}). Although not illustrated, a process {circlearound (2)} may be omitted from the illustrated method according to amethod of embodiment. That is, the eNB may provide all pieces ofinformation and/or parameters required for D2D communication ({circlearound (1)}) and TD may transmit D2D data corresponding thereto to RD(UE2) ({circle around (3)}).

In FIG. 12, the scheduling procedure may be varied according to a level(e.g., semi-statically or dynamically) of various pieces of informationand/or parameters required for D2D communication, which are provided toTD/RD from the eNB, a level (e.g., only resource allocation is signaledor all pieces of scheduling information are signaled) at which the eNBintervenes in D2D communication, and a level (e.g., through PDCCH/PDSCHor via other signaling) at which control overhead is applied to D2Dscheduling. The present invention proposes the three following D2Dscheduling methods.

Method (a): D2D Scheduling using PDSCH

In this method, an eNB may transmit D2D scheduling information to TD/RDusing a PDSCH (hereinafter, D2D-sch PDSCH). The D2D schedulinginformation may include at least a portion of, for example, TDidentification (ID), RD ID, resource allocation (RA), modulation andcoding scheme (MCS), transport block (TB) size, transmission powercontrol (TPC) command, and A/N resource information. Here, the RA mayinclude information about D2D data transmission resource and may furtherinclude information (e.g., subframe offset/index) associated with apoint of time when a D2D data transceiving operation is performed. Here,the subframe offset for D2D data transceiving may be applied based on anRA reception subframe (index). In addition, the A/N resource informationmay include A/N transmission resource information about D2D receptionand may further include information (e.g., subframe offset/index)associated with a point of time of A/N feedback transmission for D2Dreception. Here, the subframe offset for A/N transmission may be appliedbased on a D2D data transceiving subframe (index) or an RA receivingsubframe (index).

In this example, a D2D-sch PDSCH and a PDCCH for scheduling the same maybe detected/decoded by a plurality of (potential) D2D UEs. To this end,the corresponding PDCCH may be scrambled based on an RNTI (forconvenience, referred to as D2D-RNTI) that is commonly allocated to aplurality of D2D UEs. In this case, a PDSCH may include D2D schedulinginformation for a plurality of UEs. For example, the D2D schedulinginformation for a plurality of UEs may be transmitted through a mediumaccess control (MAC) protocol data unit (PDU). In this case, the MAC PDUmay include a MAC header and a MAC payload, the MAC header may include aplurality of MAC sub-headers, and the MAC payload may include aplurality of pieces of D2D scheduling information corresponding to theMAC sub-headers. Each MAC sub-header may include a D2D UE ID (e.g., TDID and RD ID).

As another method, an eNB may notify TD/RD of SF set information (and/orMCS/TB size) for making/allowing D2D signal transmission through aPDSCH, and actual D2D scheduling information such as RA (and/or MCS/TBsize), etc. may be signaled (i.e., the eNB transmits DL grant to the UEfor DL data scheduling) to RD by TD through a specific SF in thecorresponding D2D SF set. In this case, the D2D data may be transmittedto RD from TD through an SF in which corresponding D2D schedulinginformation is signaled or a specific SF thereafter.

As another method, an eNB may notify TD/RD of SF set information (and/orMCS/TB size) for making/allowing D2D signal transmission through aPDSCH, and actual D2D scheduling information such as RA (and/or MCS/TBsize), etc. may be signaled (i.e., the eNB transmits UL grant to the UEfor UL data scheduling) to TD by RD through a specific SF in thecorresponding D2D SF set. In this case, assuming that an SF in which theD2D scheduling information is signaled is SF #n, the D2D data may betransmitted to RD from TD through SF #(n+k0) or a specific SF (e.g., afirst SF of an SF set) thereafter (e.g., k0 is a positive integer (e.g.,k0≧4) and for example, k0=4).

This method may be appropriate for a situation in which a burden foroverhead and resource use for D2D scheduling is low or adynamic/adoptive change for resource and parameter required for D2D datatransmission is required.

Method (b): D2D Scheduling using 2-Step PDCCH

In this case, an eNB may transmit primary D2D scheduling information(hereinafter, D2D schd-info-1) to TD/RD using (i) PDCCH or (ii) PDSCH(similarly to the above method (a)). Here, a PDCCH for scheduling thecorresponding PDCCH or the corresponding PDSCH may be scrambled based oncommon RNTI (e.g., D2D-RNT). Then TD may transmit secondary D2Dscheduling information (hereinafter, D2D schd-info-2) to RD using aspecific control signal/channel (e.g., a control signal/channel of asimilar form to PDCCH) based on the D2D schd-info-1, and TD may transmitcorresponding D2D data to RD. In this case, corresponding D2D data maybe transmitted to RD from TD through an SF in which D2D schedulinginformation is signaled or a specific SF thereafter. As another method,RD may transmit D2D schd-info-2 to TD using a specific controlsignal/channel (e.g., a control signal/channel of a similar form toPDCCH) based on the D2D schd-info-1 and then TD may transmitcorresponding D2D data to RD. In this case, assuming that D2Dschd-info-2 is transmitted in SF #n, D2D data transmission to RD from TDmay be performed in SF #(n+k0) or a specific SF thereafter (e.g., k0 isa positive integer (e.g., k0≧4) and for example, k0=4).

Here, the D2D schd-info-1 may include (all or some of) limitedinformation such as TD ID, RD ID, RA-1, A/N resource information, etc.Here, the RA-1 may provide allocation information about a largerresource region (which may include an entire system BW) than a(frequency) resource used for actual D2D data transmission. In addition,the RA-1 may further include D2D data/control signal transceiving timeinformation. In addition, the D2D schd-info-2 may include (all or someof) limited information such as RA-2, MCS/TB size, TPC command, etc.Here, the RA-2 may provide allocation information about a resource to beused for actual D2D data transmission in a resource region (e.g., afrequency resource region) allocated by the RA-1. To this end, a D2D UEmay consider a resource region allocated by the RA-1 as an entire bandfor D2D communication and may newly number a resource index, etc. forD2D communication according to the result. By considering the allocatedresource region as an entire region for D2D communication, a bit numberrequired for resource allocation can be reduced.

That is, a control signal/channel (e.g., PDCCH-2) including D2Dschd-info-2 may be transmitted through a resource region allocated byRA-1 and D2D data may be transmitted through a resource (which ispresent in a resource region allocated by the RA-1) allocated by RA-2 inD2D schd-info-2. Here, PDCCH-2 and D2D data may be TDMed (to a symbollevel or an SF level similarly to L-PDCCH/PDSCH) on a subframe and/orFDMed (similarly to E-PDCCH/PDSCH or PUCCH/PUSCH) and transmitted. Asanother method, the RA-1 may transmit only D2D data/control signaltransceiving point of time (time) information and the RA-2 may allocateD2D data transceiving (frequency) resource information at acorresponding point of time.

This method, for example, may be appropriate for a scenario that an eNBmay allocate only a predetermined resource region/time for D2Dcommunication while the eNB cannot recognize transmission link state(e.g., CSI) between TD-versus-RD, and actual D2D scheduling (RA/MCS/TPC,etc. for D2D data transmission) and transmission is autonomouslyperformed by TD/RD.

Method (c): D2D Scheduling using Trigger

In this method, an eNB may (semi-statically) pre-configure D2Dscheduling control information to D2D UEs using a higher layer signaling(such as radio resource control (RRC)/medium access control (MAC), etc.)and may (dynamically) transmit a control signal/channel (hereinafter,referred to as D2D trigger) for triggering D2D communication to TD/RD ata specific point of time. Here, the D2D trigger may have a PDCCH formbased on the same/similar format to DCI format (e.g., 3/3A) for UL PC(power control) and DCI format (e.g., 0/1A) for DL/UL grant or may reusea PHICH (for A/N response for PUSCH transmission) for D2D trigger. Here,the PDCCH used for the D2D trigger may be scrambled based on a commonRNTI (e.g., D2D-RNTI).

When the D2D trigger has a PDCCH form for grant, D2D scheduling controlinformation configured via a higher layer signaling may include (all orsome of) RA, A/N resource information (+MCS/TB size), etc. and the D2Dtrigger may include only (all or some of) limited information such asTD/RD ID, TPC command (+MCS/TB size), etc. When the D2D trigger has aPHICH or PDCCH form for PC, D2D scheduling control informationconfigured via a higher layer signaling may include all of RA, MCS/TBsize, A/N resource information, etc., and the D2D trigger may have onlya function indicating whether D2D communication is triggered and whetherTD/RD is on or off In detail, a case of D2D trigger based on a PDCCH fora PC will be exemplified. The PDCCH for the PC includes power controlinformation of a plurality of UEs and power control information for eachUE may be provided using a bit value corresponding to each UE. Thus, inthe case of D2D trigger based on the PDCCH for the PC, it may beconsidered that 2 bits in one PDCCH scrambled based on specific D2D-RNTIare configured as a flag indicating whether TD/RD are, for example,ON/OFF respectively, or one bit in each PDCCH scrambled based on twodifferent D2D-RNTIs is configured as a flag indicating whether TD or RDis on or off respectively. When both TD/RD are OFF, it may be consideredthat D2D communication is not triggered. In addition, in the case of D2Dtrigger using a PHICH, two different PHICH resources may be configuredas a flag indicating whether TD/RD is on or off A/N modulation on eachPHICH resource may be used for ON/OFF signaling.

As another method, an eNB may perform D2D triggering at a specific pointof time while SF set information (and/or MCS/TB size) formaking/allowing D2D signal transmission is pre-configured for TD/RD viaa higher layer signaling. In this case, actual D2D schedulinginformation such as RA (and/or MCS/TB size), etc. may be signaled (i.e.,the eNB transmits DL grant to the UE for DL data scheduling) to RD by TDthrough a specific SF in the D2D SF set. Corresponding D2D data may betransmitted to RD from TD though an SF through an SF in which D2Dscheduling information is signaled or a specific SF thereafter.

As another method, an eNB may perform D2D triggering at a specific pointof time while SF set information (and/or MCS/TB size) formaking/allowing D2D signal transmission is pre-configured for TD/RD viaa higher layer signaling. In this case, actual D2D schedulinginformation such as RA (and/or MCS/TB size), etc. may be signaled (i.e.,the eNB transmits DL grant to the UE for UL data scheduling) to TD by RDthrough a specific SF in the D2D SF set. Assuming that an SF in whichthe D2D scheduling information is signaled is SF #n, the correspondingD2D data may be transmitted to RD from TD through SF #(n+k0) or aspecific SF (e.g., a first SF of an SF set) thereafter (e.g., k0 is apositive integer (e.g., k0≧4) and for example, k0=4).

In this method, this method may be appropriate for a situation in whichchange in D2D data transmission resources and parameters is relativelyintermittent or a burden for overhead and resource use for D2Dscheduling is high.

(2) Resource Allocation Method for D2D Communication

As described above, it may be considered that, during D2D communication,an eNB explicitly notifies TD/RD of information associated with D2D datatransmission time and/or A/N feedback transmission time for D2Dreception through a PDCCH, etc. However, whenever D2D communication isperformed, if the information associated with the D2D data transmissiontime and/or the A/N feedback transmission time for D2D reception aredynamically signaled, overhead may be caused. Blind decoding (BD) may beincreased due to increase in DCI format size. In addition, when feedbackfor D2D reception is NACK, if the eNB transmits D2D scheduling controlinformation for retransmission of D2D data, overhead may also be caused.To prevent this, RD may transmit A/N feedback to TD and reuse automaticretransmission timing in legacy 3GPP Rel-10 without changes. However, ingeneral, since A/N feedback transmission to an eNB is not performed inD2D communication, when a conventional retransmission method is usedwithout changes, the eNB cannot know when D2D data transmission issuccessful, and thus the eNB need to continuously empty a retransmissionresource instead of allocating the retransmission resource to anotherUE. Accordingly, when a conventional retransmission method is used inD2D communication without changes, problems may arise in that ascheduling restriction to other UEs (that do not participate in D2Dcommunication) becomes more serious. In addition, D2D data/feedbacktransmission time may need to be shared by other (potential) D2D) UEs aswell as TD/RD that actually perform D2D communication (e.g., in order toallow detection/measurement/report, etc. of D2D signal andinterference).

Accordingly, the present invention proposes that D2D data (and/orcontrol signal) and a potential D2D candidate SF set (i.e., a D2D SFset) in which feedback transmission is to be performed are configured(via a higher layer signaling such as broadcast/RRC, etc.).

FIG. 13 illustrates a D2D communication procedure according to anembodiment of the present invention. Referring to FIG. 13, a UE (UE N orUE M) that participate in D2D communication may receive D2D subframe setallocation information from a BS (S1302). That is, a plurality of SFsets (e.g., an SF set for UE-BS communication and one or more SF set forD2D communication) may be configured for a D2D UE, and the D2D UE maytransmit and receive a D2D signal in an SF set for D2D communication(S1304).

In detail, a common D2D SF set or a separate D2D SF set may beconfigured for D2D data transmission and reception (to RD from TD)(and/or D2D scheduling information signaling/detection (to RD from TD orto TD from RD)) and D2D reception A/N feedback (to TD from RD). That is,an SF for D2D data transmission and reception (and/or D2D schedulinginformation transmission and reception) and an SF set for A/N feedbackmay be the same or may be independently configured. The SF for D2D datatransmission and reception (and/or D2D scheduling informationtransmission and reception) and the SF set for A/N feedback maypartially overlap each other. Alternatively, the SF for D2D datatransmission and reception, the SF set for D2D scheduling informationtransmission and reception, and the SF set for A/N feedback may beentirely or partially the same or may be independently configured. TheSF for D2D data transmission and reception, the SF set for D2Dscheduling information transmission and reception, and the SF set forA/N feedback may entirely or partially overlap each other. In addition,for configuration of a D2D SF set, a cell-specific D2D SF set (ahatching box) including a potential D2D SF of all D2D UEs in a cell maybe present, and a specific subset in a cell-specific D2D SF set may beconfigured as a UE-specific D2D SF set constituting a D2D candidate SFof each UE (a hatching box with a bold outline).

Meanwhile, in the legacy 3GPP Rel-10, a specific SF may be intentionallyconfigured for MBSFN, a legacy UE may be intentionally faked to performan operation such as detection/measurement, etc. of a main signal (e.g.,CRS) and a channel (e.g., a PDCCH) only in a limited small number (1 and2) OFDM symbol periods of a front portion of a corresponding SF, andthen UE-specific DMRS-based DL data transmission support for providingmore enhanced performance may be considered for an advanced UE throughthe remaining periods except for the corresponding symbol period.Accordingly, the present invention proposes that an entire or partialportion of an MBSFN SF (set) is configured (used) as the D2D candidateSF (set). In this case, it may be possible to limit a maindetection/measurement operation of another UE (which is a legacy UE or aUE that does not participate in D2D) within a limited small number ofsymbol periods and to configure D2D communication (data/feedback) linkwithout serious interference/error due to D2D signals through theremaining periods.

FIG. 14 illustrates a D2D communication procedure according to anembodiment of the present invention. FIG. 14 illustrates a procedure oftransmitting D2D data and feedback based on a D2D SF set.

Referring to FIG. 14, when TD/RD receives D2D scheduling controlinformation (using a method such as PDSCH/PDCCH and D2D trigger, etc.for the D2D scheduling triggering) from an eNB in SF #n (e.g., SF #2)(S1402), D2D data (and/or D2D scheduling information includingcorresponding RA (and/or MCS/TB size), etc.) may be transmitted to RDfrom TD through SF # (n+k1) or a next closest D2D SF (i.e., SF #m (e.g.,SF #4)) (for data transmission). Then when RD receives D2D data from TDin SF #m (e.g., SF #4), A/N feedback therefor may be transmitted toTD/eNB from RD through SF # (m+k2) (e.g., SF #(4+4)) or a next closestD2D SF (i.e., SF #h (e.g., SF #16)) (for A/N feedback). Then when TDreceives NACK from RD in SF #h (e.g., SF #16), D2D data correspondingthereto may be retransmitted through SF # (h+k3) (e.g., SF #(16+4)) or anext closest D2D SF (for data transmission). Here, k1 to k3 may be apositive integer (e.g., k1=k2=k3≧4) and for example, k1=k2=k3=4.

As another method, it may be possible to configure D2D schedulinginformation signaling performed through SF #m and a D2D datatransmission corresponding to the D2D scheduling information signalingas follows. First, RD may signal D2D scheduling information including RA(and/or MCS/TB size), etc. to TD in SF #m and TD may transmit D2D datacorresponding to corresponding information to RD in next SF #(m+k5) ornext closest D2D SF #m1 (e.g., k5 is a positive integer (e.g., k5≧4) andfor example, k5=4).

Meanwhile, it may be possible to request information such as RA (and/orMCS/TB size), etc. and (preferred) SF appropriate to apply D2D datatransmission directly to an eNB by TD and/or RD (which relatively wellrecognizes D2D link state/quality).

In addition, an independent D2D discovery SF set may be configured (viaa higher layer signaling such as broadcast/RRC, etc.) in order toperform only detection/measurement/report of D2D signal and interference(or on a subset of a corresponding SF set) separately from D2D data(and/or a control signal) and a D2D SF set for feedback. In this case,similarly, when a control signal/channel indicatingdetection/measurement of D2D signal and interference is received throughSF #g, detection/measurement of D2D signal and interference may beperformed through SF # (g+k4) or a next closest D2D discovery SF (k4 isa positive integer (e.g., k4≧0)). Alternatively, upon receiving acontrol signal/channel indicating transmission of a D2D discovery signalthrough SF #g (in order to discover a corresponding specific D2D UE byother D2D UEs), a specific D2D UE may transmit the D2D discovery signalthrough SF #(g+k6) or a next closest D2D discovery SF (e.g., k6 is apositive integer (e.g., k6≧4) and for example, k6=4).

In addition, in order to ensure discovery performance for a D2D signalof an entire D2D UE group that performs D2D communication, a UE mayomit/abandon transmission of a periodic signal/channel (e.g., a periodicSRS, a PUCCH for transmission of periodic CSI, a PUCCH for transmissionof an SR, and a PUSCH scheduled in an SPS manner) which is set/reservedto be transmitted in a D2D discovery SF set and/or a PUSCH that isautomatically retransmitted (non-adaptively based on only PHICH NACK)through the corresponding D2D discovery SF set. In addition, the UE mayoperate on an assumption that the UE does not expect grant (e.g., ULgrant for scheduling PUSCH transmission) and/or a command (e.g., a PDCCHorder for command of RACH preamble transmission) for scheduling asignal/channel to be transmitted in a D2D discovery SF set and/or grant(e.g., DL grant for scheduling PDSCH transmission) causing HARQ-ACKPUCCH transmission in a D2D discovery SF set or an assumption that theyare not transmitted. For example, the UE may omit a DL grant PDCCHreception process for an SF, HARQ-ACK transmission timing of whichcorresponds to the D2D discovery SF set, or may disregard or may notdecode a PDSCH corresponding to a PDCCH even if the UE receives the DLgrant PDCCH. Meanwhile, the UE may omit a UL grant PDCCH receptionprocess for an SF, PUSCH transmission timing of which corresponds to theD2D discovery SF set, or may perform a reception process on a UL grantPDCCH and drop PUSCH transmission when a PUSCH transmission point oftime corresponding to a UL grant PDCCH is included in a D2D discovery SFset.

Alternatively, conversely, upon detecting/receiving grant and/or commandfor scheduling a signal/channel to be transmitted in a specific D2Ddiscovery SF and/or grant causing HARQ-ACK PUCCH transmission in aspecific D2D discovery SF, a UE may omit D2D signaldetection/measurement in the corresponding specific D2D discovery SF andcan operate while assuming/considering the corresponding SF as a normalSF that is not set as a D2D discovery SF.

The aforementioned signal/channel processing procedure can also beapplied in the same/similar way to a D2D SF set that is set for D2D datatransmission and reception and/or D2D scheduling informationtransmission and reception and/or D2D reception A/N feedback.

(3) Modulation and Demodulation Method for D2D Communication

A UE for supporting a D2D operation may further include an OFDMtransmitting module and/or an SC-FDM receiving module for D2Dcommunication according to category/capability as well as an OFDMreceiving module and an SC-FDM transmitting module for communicationwith an eNB. When hardware specification (e.g., the characteristics of apower amplifier) is sufficiently stable, D2D communication link thatoperates based on OFDM transmission and reception can be more effective.In addition, like prior art, it may be necessary to support D2Dcommunication for a low-specification UE configured with only an OFDMreceiving/SC-FDM transmitting module.

Hereinafter, a method for configuring/determining a data modulation anddemodulation method for D2D signal transmission and reception will beproposed. First, a UE may notify an eNB of information (e.g., fastFourier transform (FFT) size) about added specification (OFDMtransmitting/SC-FDM receiving module) for D2D use in addition to basicspecification (OFDM receiving/SC-FDM transmitting module). In this case,an applicable bandwidth (BW) of the added OFDM transmitting/SC-FDMreceiving module may be smaller than an applicable BW of the basic OFDMreceiving/SC-FDM transmitting module. In detail, whether OFDM modulationand demodulation (e.g., a PDSCH, or PDCCH/PDSCH when transmission ofscheduling control information is also considered on D2D link like in(b) above) or SC-FDM modulation and demodulation (e.g., PUSCH, orPUCCH/PUSCH when transmission of scheduling control information is alsoconsidered on D2D link like in (b) above) is applied for D2D datatransmission and reception on D2D communication link may be setcell-specifically or UE-specifically via broadcast/RRC/L1(Layer1)/L2(Layer 2) signaling, etc. In addition, in the above method, it maybe possible to indicate a modulation and demodulation method in D2Dtrigger and PDSCH/PDCCH for triggering D2D scheduling. In addition, itmay be possible to apply an OFDM modulation and demodulation method whena PDCCH for D2D triggering is based on DCI format for DL grant and toapply an SC-FDM modulation and demodulation method when a PDCCH for D2Dtriggering is based on DCI format for UL grant. In addition, it may bepossible to apply an OFDM modulation and demodulation method whenperformance of transmission and reception of D2D data is indicatedthrough a DL SF and to apply an SC-FDM modulation and demodulationmethod when performance of transmission and reception of D2D data isindicated through a UL SF.

CP configuration information for D2D signal transmission may be set viabroadcast/RRC/L1/L2 signaling or indicated through PDSCH/PDCCH and D2Dtrigger for D2D scheduling triggering. For example, the CP configurationinformation may indicate CP length information, for example, whethernormal/extended CP, and/or a specific CP (e.g., CP shorter than normalCP) added dedicatedly for D2D.

In addition, start/end time information (e.g., a symbol position/indexfor start/end of D2D signal transmission in the corresponding SF) of D2Dsignal transmission in a D2D (discovery) SF may be set viabroadcast/RRC/L1/L2 signaling or indicated via PDSCH/PDCCH and D2Dtrigger for D2D scheduling triggering. For example, assuming that symbolindexes in one SF are configured as being 0 to K, a symbol index n and min the D2D (discovery) SF may be set/indicated as start/end point oftime of D2D signal transmission (0≦n≦K, 0≦m≦K, and n<m). Inconsideration of transmission and reception operation switching time(i.e., switching time) and/or propagation delay of a (relatively short)D2D transmission signal that may be different from link between an eNBand a UE, when n is set as a specific value or less (e.g., 0),transmission and reception of all or (last) some of symbols of an SFimmediately before the corresponding D2D SF may be limited/omitted. Forthe same reason, when m is set as a specific value or more (e.g., K),transmission and reception of all or (first) some of symbols of an SFimmediately before the corresponding D2D SF may be limited/omitted.

In addition, when D2D transmission and reception is performed through aDL SF, a D2D data/control signal may be rate-matched for an OFDM symbolor a resource element (RE) that includes or can include transmission ofcommon reference signal (CRS)/channel state information reference signal(CSI-RS) and/or demodulation reference signal (DMRS) between an eNB and(another) UE. In addition, when D2D transmission and reception isperformed through a UL SF, the D2D data/control signal may berate-matched for an SC-FDM symbol or an RE that includes or can includetransmission of a sounding reference signal (SRS) and/or DMRS. Inaddition, when D2D transmission and reception is performed through aDL/UL SF, DMRS for D2D signal reception/demodulation may be arranged soas not to overlap with DMRS in 3GPP Rel-10 on the time axis and/orfrequency axis in order to prevent interference with other UEs (whichcommunicate with an eNB). For example, in the case of normal CP based ULSF in 3GPP Rel-10, DMRS for PUSCH is arranged in a fourth SC-FDM symbolin each slot. In this regard, when D2D data transmission and receptionbased on SC-FDM modulation and demodulation is performed through thecorresponding UL SF, DMRS for D2D may be arranged in, for example, athird or fifth SC-FDM symbol (among the remaining symbols except for thefourth symbol) in each slot. In addition, considering that D2D datatransmission and reception can be mainly performed between UEs with lowmobility, DMRS for D2D signal reception/demodulation can be formed insuch a way that some symbols are omitted in the DMRS structure in 3GPPRel-10. For example, in the case of normal CP based UL SF in 3GPPRel-10, one SC-FDM symbol in each slot is arranged as DMRS for PUSCH. Inthis regard, when D2D data transmission and reception based on SC-FDMmodulation and demodulation is performed through the corresponding ULSF, DMRS for D2D may be arranged only in one specific slot (e.g., firstor second slot).

In a D2D scheduling method in addition to the above proposals, D2Dscheduling control information (which is transmitted throughPDSCH/PDCCH, D2D trigger, etc. or is previously set via RRC, etc.) mayinclude D2D data transmission/retransmission allowance duration and SFset, allowance transmission/retransmission number of times (i.e.,maximum reTx), etc. The TD/RD that receives them may transmit/retransmitD2D data by a number of times corresponding to the corresponding maximumreTx only in the corresponding duration/SF set. In this case, the RD maytransmit A/N feedback for D2D data reception to an eNB (i.e.,A/N-to-eNB) or the TD (A/N-to-TD). When all of the duration/SFset/maximum reTx are not used, if the RD successfully receives D2D(i.e., A/N feedback is ACK), information (e.g., corresponding A/Nfeedback) about this may be signaled to the TD from the eNB (in the caseof A/N-to-eNB) or to the eNB from the TD (in the case of A/N-to-TD). Assuch, the TD can reuse an SF that is not used in the receivedduration/SF set/maximum reTx for communication with the eNB. Inaddition, the eNB can reallocate the SF that is not used in theduration/SF set/maximum reTx to another UE. In the above case, when thetransmission/retransmission allowance SF set is indicated, SFs in thecorresponding set may be configured with an appropriate time interval(i.e., so as to sequentially perform D2D transmission=>A/Nfeedback=>corresponding information signaling=>D2D retransmission) inconsideration of latency used for related information signaling and A/Nfeedback.

FIG. 15 illustrates a BS 110 and a UE 120 to which an embodiment of thepresent invention is applicable. In the case of a system including arelay, the BS 110 or the UE 120 may be replaced by the relay. In UE-UElink, the illustrated BS-UE may be replaced by UE-UE.

Referring to FIG. 15, a wireless communication system includes the BS110 and the UE 120. The BS 110 includes a processor 112, a memory 114,and a radio frequency (RF) unit 116. The processor 112 may be configuredto embody the procedures and/or methods proposed by the presentinvention. The memory 114 is connected to the processor 112 and storesvarious pieces of information associated with an operation of theprocessor 112. The RF unit 116 is connected to the processor 112 andtransmits and/or receives a radio signal. The UE 120 includes aprocessor 122, a memory 124, and an RF unit 126. The processor 122 maybe configured to embody the procedures and/or methods proposed by thepresent invention. The memory 124 is connected to the processor 122 andstores various pieces of information associated with an operation of theprocessor 122. The RF unit 126 is connected to the processor 122 andtransmits and/or receives a radio signal. The BS and/or the UE 120 mayeach have a single antenna or a multiple antenna.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). A specific operationdescribed as performed by the BS may be performed by an upper node ofthe BS. Namely, it is apparent that, in a network comprised of aplurality of network nodes including a BS, various operations performedfor communication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘access point(AP)’, etc. In addition, the term ‘terminal’ may be replaced with theterm ‘UE’, ‘mobile station (MS)’, ‘mobile subscriber station (MSS)’,‘subscriber station (SS)’, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof In a hardware configuration, an embodiment of the presentinvention may be achieved by one or more application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSDPs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of theinvention should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a wireless communicationapparatus such as a user equipment (UE), a relay, a base station (BS),etc.

The invention claimed is:
 1. A method for transmitting Device-to-Device(D2D) data by a first user equipment (UE) in a wireless communicationsystem, the method comprising: receiving, by the first UE, a RadioResource Control (RRC) message including Subframe (SF) set allocationinformation from a base station, the SF set allocation informationindicating non-contiguous SF sets for D2D communication; receiving, bythe first UE, a first Physical Downlink Control Channel (PDCCH)including primary D2D scheduling information from the base station in asubframe #n, wherein n is an integer of 0 or more; transmitting, by thefirst UE, a second PDCCH including secondary D2D scheduling informationto a second UE using the primary D2D scheduling information; andtransmitting, by the first UE, the D2D data to the second UE using thesecondary D2D scheduling information, in a first available one of thenon-contiguous SF sets for D2D communication after a subframe #(n+k1),wherein k1>0.
 2. The method according to claim 1, wherein a CyclicRedundancy Check (CRC) of the first PDCCH is scrambled with a commonRadio Network Temporary Identifier (RNTI) for D2D.
 3. The methodaccording to claim 1, wherein a frequency resource indicated by thesecondary D2D scheduling information is allocated on an assumption thata frequency resource indicated by the primary D2D scheduling informationis an entire frequency resource for D2D communication.
 4. The methodaccording to claim 3, wherein the primary D2D scheduling informationindicates a plurality of frequency resource indexes, and the pluralityof frequency resource indexes are renumbered for the secondary D2Dscheduling information.
 5. The method according to claim 4, wherein afield size of the secondary D2D scheduling information is smaller than afield size of the primary D2D scheduling information.
 6. A first userequipment (UE) configured to perform Device-to-Device (D2D) operationsin a wireless communication system, the first UE comprising: a radiofrequency (RF) unit configured to transmit and receive a radio signal;and a processor operably coupled with the RF unit and configured to:receive a Radio Resource Control (RRC) message including Subframe (SF)set allocation information from a base station, the SF set allocationinformation indicating non-contiguous SF sets for D2D communication,receive a first Physical Downlink Control Channel (PDCCH) includingprimary D2D scheduling information from the base station in a subframe#n, wherein n is an integer of 0 or more, transmit a second PDCCHincluding secondary D2D scheduling information to a second UE using theprimary D2D scheduling information, and transmit the D2D data to thesecond UE using the secondary D2D scheduling information, in a firstavailable one of the non-contiguous SF sets for D2D communication aftera subframe #(n+k1), wherein k1>0.
 7. The first UE according to claim 6,wherein a Cyclic Redundancy Check (CRC) of the first PDCCH is scrambledwith a common Radio Network Temporary Identifier (RNTI) for D2D.
 8. Thefirst UE according to claim 6, wherein a frequency resource indicated bythe secondary D2D scheduling information is allocated on an assumptionthat a frequency resource indicated by the primary D2D schedulinginformation is an entire frequency resource for D2D communication. 9.The first UE according to claim 8, wherein the primary D2D schedulinginformation indicates a plurality of frequency resource indexes, and theplurality of frequency resources indexes are renumbered for thesecondary D2D scheduling information.
 10. The first UE according toclaim 8, wherein a field size of the secondary D2D schedulinginformation is smaller than a field size of the primary D2D schedulinginformation.